Field of the Invention
The present invention relates to an apparatus and method for metering delivery quantity of an ultra-low temperature liquefied gas.
For example, liquefied natural gas (hereinafter referred to as LNG), which is an ultra-low temperature liquefied gas, is used for power generation and the like. It is usually cooled and stored at about xe2x88x92162xc2x0 C., and is delivered by means of a tank lorry or a container-type LNG tank. On the delivery of LNG, the flow rate in loading is regulated manually, and also metering is performed using a truck scale.
Conventionally, for example, as shown in FIG. 2, after the pressure of LNG is reduced to about 0.4 MPa(G) by using a pressure reducing valve 201, loading work has been performed while the flow rate is directly regulated by manual operation or a flow indicating controller (FIC) 202 is set appropriately by manual operation.
On the other hand, LNG produces much gas unless the cooling temperature thereof is kept, resulting in hindrance to the loading operation. Therefore, a circulation path for LNG gas is provided separately from a path for loading operation so as to return LNG gas to an LNG tank (not shown) as a return gas through a throttle valve 203. Thereby, the temperature of a pipe just before the flow indicating controller 202 is kept low. With the progress in the operation for loading LNG into a tank lorry 204, a gas component produced along with the loading operation is discharged into a pipe 205.
Before and after the loading operation, a purge gas such as nitrogen gas having an original pressure of about 0.7 MPa(G) is sent into a loading flow path, and is then sealed in under a pressure of about 0.2 MPa (G) to maintain the dried condition in the pipe.
When such a loading operation as shown in FIG. 2 is performed, the metering of delivery quantity has been performed by metering the tank lorry 204 before and after the loading operation by using the truck scale.
Therefore, the tank lorry 204 must be caused to pass through the truck scale before and after the receipt of LNG, which is troublesome in operation. Especially when the tank lorry 204 is caused to pass through the truck scale without backward motion or when an arrangement plan for causing the tank lorry 204 to pass through a loading island is made, there is a problem of increased constraint. Also, an operator""s job for monitoring and regulating the delivery quantity is needed, so that the burden in operation is heavy.
On the other hand, for petroleum and LPG (propane gas), an automatic loading system has been used. In this system, the quantity of flow of loaded LPG and the quantity of flow of return gas are measured, and the integrated value of the difference therebetween is obtained automatically as the delivery quantity. However, for LNG, which has a very low boiling point, unless a delivery quantity metering system is sufficiently cooled in advance, gas is liable to be produced. Therefore, even if the automatic loading system for LPG is used as it is, the metering accuracy cannot be obtained, so that the automatic loading system has not been used for LNG so far.
The present invention has been made in view of the above situation, and accordingly an object thereof is to provide an apparatus for metering delivery quantity of an ultra-low temperature liquefied gas that realizes an automatic metering loading system and a method therefor.
Specifically, in the present invention, there is provided a flow path for performing an operation for circulating the ultra-low temperature liquefied gas before the start of loading from two viewpoints of precooling a metering system and maintaining the measurement range of a loading flowmeter, and the circulation (return) quantity of flow is deducted from the loading quantity of flow, by which highly accurate automatically integrated metering is realized in all processes for delivery.
In one aspect of present invention, there is provided an apparatus for metering delivery quantity of an ultra-low temperature liquefied gas delivered from a storage element to a transportation element, comprising a flow path for the ultra-low temperature liquefied gas circulating from the storage element to the storage element; at least two flowmeters provided in the flow path; and a flow path, which is provided between the two flowmeters, for supplying the ultra-low temperature liquefied gas to the transportation element.
The apparatus for metering delivery quantity of an ultra-low temperature liquefied gas in accordance with the present invention preferably comprises a gas flowmeter provided in a flow path for return gas returned from the transportation element. Further, in the present invention, there is preferably provided a batch controller for monitoring the flow information sent from the flowmeters, whereby fully automatic control is accomplished. Also, the flowmeters preferably are what we call a Coriolis-type flowmeter.
In another aspect of the present invention, there is provided a method for metering delivery quantity of an ultra-low temperature liquefied gas in another aspect. Specifically, it provides a method for metering delivery quantity of an ultra-low temperature liquefied gas delivered from a storage element to a transportation element, comprising the steps of circulating the ultra-low temperature liquefied gas in a flow path from the storage element to the storage element; measuring the loading quantity of flow to the transportation element and the return quantity of flow to the storage element by using at least two flowmeters provided in the flow path; and supplying the ultra-low temperature liquefied gas to the transportation element through a flow path provided between the two flowmeters.
The method for metering delivery quantity of an ultra-low temperature liquefied gas in accordance with the present invention preferably comprises the step of measuring the quantity of return gas by using a gas flowmeter provided in a flow path for return gas returned from the transportation element. Further, in the present invention, the flow information sent from the flowmeters is preferably monitored by a batch controller, whereby fully automatic control is accomplished.
In the specification and in the attached claims, xe2x80x9cultra-low temperature liquefied gasxe2x80x9d is a concept including liquid nitrogen, liquid oxygen, liquid ethylene, and the like in addition to LNG.
In the specification and in the attached claims, xe2x80x9cstorage elementxe2x80x9d means a vessel for storing an ultra-low temperature liquefied gas, and generally means a storage tank.
In the specification and in the attached claims, xe2x80x9ctransportation elementxe2x80x9d means a means for transporting an ultra-low temperature liquefied gas, and generally means a tank lorry or a container-type ultra-low temperature liquefied gas storage tank.